1. Field of the Invention
The present invention is directed to a dynamically balanced appartus having a reciprocating member driven by an electric motor, and more particularly a dynamically balanced shaver of reciprocatory type driven by the motor.
2. Description of the Prior Art
It is well known in the art to provide dynamic balancing of an apparatus having a reciprocating member for eliminating excess vibration, as seen in U.S. Pat. No. 4,167,060, which discloses an electric shaver of reciprocatory type including an inner cutter driven by an electric motor through a mechanism of translating rotary motion of the motor into reciprocatory motion of the inner cutter. This patent utilizes an eccentric flyweight as a counterbalance which is mounted on the end of an output shaft of the motor in order to provide dynamic balance for offsetting the vibration or inertia force developed by the reciprocating motion of the inner cutter. Considering that such eccentric flyweight rotates around the axis of the motor output shaft in a circular orbit, it produces, in addition to the vibratory motion in the reciprocating direction of the cutter, another vibratory motion or inertia force in a direction perpendicular to the reciprocating direction of the inner cutter so as to cause undesired vibration in that direction. In this sense, the patent is not completely satisfactory and effective in eliminating the vibration in all directions.
To solve this problem, it has been contemplated by the same inventor of the present invention to add a separate counterweight to the above mechanism for offsetting the undesired vibratory motion of the eccentric flyweight, as shown in Japanese Publication (KOKAI) No. 54-76358 of 1979 of Unexamined Patent application. The added counterweight is held on one end of a resilient plate having the other end fixed to a shaver housing. The resilient plate is operatively connected to the motor output shaft adjacent to the eccentric flyweight in such a way as to be movable together with the counterweight in the direction perpendicular to the reciprocating direction of the inner cutter upon rotation of the motor shaft, eliminating the undesired vibration in the direction perpendicular to the reciprocating direction of the inner cutter.
Although the above scheme well eliminates the undesired vibration and therefore the fatigue of the user grasping the shaver, there arises another problem that the added counterweight requires more spacing on the lateral side of the eccentric flyweight to thereby increase unduly the lateral dimension of the shaver, since the added counterweight is disposed at a location spaced laterally away from the eccentric flyweight in the direction perpendicular to the reciprocating path of the inner cutter. In view of the above, it has been mostly desired to add the counterweight without causing any substantial increase in the shaver dimensions, particularly in the lateral dimension thereof.